How to Test a Coil Pack or Ignition Coil?

　　Professionals often use the term coil group to describe any type of modern ignition coil. However, by definition, a coil set is a set of ignition coils combined in a molded block. With this design, each cylinder has its own ignition tower, but shares the coil with a matching cylinder.

　　This is different from the more commonly used Coil on Plug (COP) ignition system. In the COP system, each cylinder has its own ignition coil, located on top of the spark plug.

　　However, for convenience, we will refer to both designs as ignition coils in this article.

　　Note: We will not cover distributor-type ignition systems that use only one coil.

　　Although testing ignition coils can be tricky, it is feasible if you have the tools and knowledge. Here are six different ways to help you get the job done.

　　Perform a visual inspection

　　In some cases, you can find a damaged ignition coil through a simple visual inspection. Issues such as cracks, burn marks, and carbon tracking all indicate a problem with the coil.

　　Replace the suspicious ignition coil to another cylinder

　　If your car has a separate ignition coil (or a package that combines only two coils), you can replace the suspicious ignition coil with another cylinder to see if a misfire occurs.

　　What if you don’t have a scanning tool or barcode reader? In many cases, you can perform a power balance test to offset each cylinder. When each cylinder is cut off, you will want to hear the RPM drop. Cylinders with little or no change in RPM are problematic and cannot be fully functional.

　　Remember: the RPM drop of a particular cylinder may be caused by other problems (ie, fuel delivery or engine mechanical problems) besides damaged coils. In order to verify whether the coil is the culprit, you need to change the coil to another cylinder and repeat the power balance test. If the lost contribution moves with the coil, the ignition coil is faulty.

　　Note: Never perform a power balance test by disconnecting the spark plug wires. It may cause damage to the vehicle and serious injury.

　　Use a spark tester

　　You can also use a spark tester to test the ignition coil. The tool is installed in the ignition coil to determine whether the coil generates sparks.

　　Note: If none of the ignition coils produces sparks, the problem may be on the control side (primary side) of the ignition system, rather than a single ignition coil. The absence of sparks from an ignition coil indicates that the coil is broken.

　　Not all spark testers are suitable for all types of ignition systems, so be sure to choose the right tool for your application. It is also a good idea to obtain a high-quality, adjustable spark tester. Inexpensive non-adjustable testers can be misleading, because sometimes they still emit weak sparks.

　　The steps to use a spark tester will vary, depending on the tool you use and the type of ignition system in your car. But the following video will give you an idea of ​​what is involved:

　　You may hear someone suggest to remove the spark plug and ground it instead of using a spark tester. The problem is that the voltage required to ignite the spark plug removed from the engine is lower than the spark plug that is still installed.

　　Therefore, although you may have sparks, skipping the plug gap while the engine is running may not be enough.

　　On the other hand, high-quality spark testers require tens of thousands of volts to ignite. Therefore, the tool can accurately measure whether there are enough sparks to skip the plug gap.

　　In addition, using a spark tester is safer than grounding the plug.

　　Use coil plug (COP) probe

　　The coil on plug (COP) probe is a tool that uses a phenomenon called magnetic induction to clearly indicate whether the COP coil is igniting. Some COP probes simply flash a light to indicate that the coil is working, while others display data on the screen.

　　It is easy to use the COP probe. Just follow the product instructions for the setup and place the paddle end of the tool on the coil. For flash probes, if the coil is triggering, the tool will light up.

　　Check the resistance of the ignition coil

　　Measuring the resistance of the ignition coil used to be a popular test method. The procedure includes using a digital multimeter (set to ohms) to check the resistance of the primary and secondary windings in the coil. Comparing the results with the manufacturer's specifications should indicate the quality of the coil.

　　But resistance testing has fallen out of favor because it is not always decisive. Since you are not monitoring the coil when it is heated or under load, a bad coil may pass the resistance test. In addition, fewer and fewer car manufacturers list coil resistance specifications in their maintenance information.

　　There is no doubt that an oscilloscope is the best tool for diagnosing any type of ignition system problem, including broken coils.

　　The oscilloscope can be used to display the waveform pattern of the ignition system signal voltage as a function of time. The disadvantage is that ranges are usually expensive to purchase and many people find them difficult to use.